Synchronizing device in a vehicle gearbox

ABSTRACT

A synchronizer in a vehicle gearbox includes a synchronizing ring and a torque-transmitting element, which transmits a torque from the synchronizing ring to an engaging sleeve in such a manner that the engaging sleeve is imparted an extra force in the engaging direction.

BACKGROUND OF THE INVENTION

The present invention relates to a synchronizer in a vehicle gearbox,comprising a guide sleeve intended to be non-rotatably joined to a shaftin the gearbox, an engaging sleeve which is non-rotatably, but axiallydisplaceably, mounted on the guide sleeve, an engaging ring providedwith exterior engaging teeth and which is intended to be solidly joinedto a gear rotatably mounted on said shaft and is lockable relative tothe guide sleeve by axial displacement of the engaging sleeve from aneutral position to an engagement position, in which interior engagingteeth on the engaging sleeve engage the exterior teeth on the engagingring, and a synchronizing ring cooperating with the engaging sleeve andthe engaging ring, said synchronizing ring having a conical frictionalsurface which is movable to engagement with a facing conical frictionalsurface on the engaging ring.

DESCRIPTION OF THE RELATED ART

In heavy vehicle gearboxes there is often a need to increase thesynchronizing torque above what is normally obtained with a commonsimple synchronization, in order to reduce the shifting effort andeliminate the risk of wear injury to the back and shoulders ofprofessional truck drivers. One method of increasing the synchronizingtorque and thus reducing the shifting effort is to arrange a so-calleddouble synchronization, i.e. a synchronizer with two concentricsynchronizing rings for each releasable running gear. A doublesynchronization reduces the shifting effort on the shift lever by about30% in comparison to a corresponding single synchronization, but itinvolves an increase in the manufacturing costs of the gearbox which isnot insignificant. Another method is to increase the length of stroke ofthe shift lever to increase the mechanical advantage, but thispresupposes that there is space available so that the driver will notrisk hitting his knuckles on surrounding components in the cab. A longstroke also creates problems in trucks having the engine and gearboxplaced under a tiltable cab.

A third method is to use a pneumatic or hydraulic servo unit but this isan expensive solution.

SUMMARY OF THE INVENTION

The purpose of the present invention is to achieve a synchronizer of thetype described by way of introduction, by means of which it is possible,while retaining the short shift length for the gear lever, and withouthaving to use a servo unit, to reduce the shifting force which isnecessary to apply to the gear lever, to a fraction of that needed forshifting in hitherto known gearboxes with synchronizers of the typedescribed by way of introduction.

This is achieved according to the invention by virtue of the fact thatthe synchronizing ring is fixed rotationally relative to atorque-transmitting element, has cam surfaces which cooperate with camsurfaces on the engaging sleeve and which upon relative rotation betweenthe torque-transmitting element and the engaging sleeve--caused byfrictional engagement between the frictional surfaces of thesynchronizing ring and of the engaging ring--create a force acting onthe engaging sleeve in the engaging direction.

The invention is based on the idea of transmitting a portion of therotational energy of the gearbox itself to the shifting mechanism and inthis manner creating a type of integrated servo system which assists themanually initiated and terminated shifting process. In principle,shifting, after manual initiation of the synchronizing process, can beeffected entirely by the servo system created. This is, however, incertain cases not desirable since it might cause unintentional shifting.

In a further development of the synchronizer according to the invention,the torque-transmitting element is displaceable away from thesynchronizing ring against the effect of a spring force, which in apreferred embodiment is generated by a spring washer package between asurface of the torque-transmitting element and a facing surface on theguide sleeve. By selecting the spring characteristic for the compressedspring package it is possible to limit the force which can betransmitted axially to the engaging sleeve.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail below with reference toexamples shown in the accompanying drawings, where FIG. 1 shows afragmented end view of a synchronizer according to the invention, FIGS.2a and 2b show a longitudinal section and a plan view of thesynchronizer in FIG. 1 with the components in the neutral position, FIG.3 is a view corresponding to FIG. 2b with the components shown duringtheir blocking phase, FIGS. 4a and 4b are views corresponding to FIGS.2a and 2b with the components in the synchronizing phase, FIG. 5 is afragmented end view with the components in the synchronizing phase,FIGS. 6 and 7 show the components during the twisting loose and engagingphases, respectively, and FIGS. 8A and 8B show a longitudinal sectionand a plan view, respectively, of a second embodiment of a synchronizeraccording to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The synchronizer according to the invention comprises a guide sleeve 1non-rotatably on a shaft (not shown) in a gearbox. The guide sleeve 1has outer teeth 2, which engage in spaces between inward teeth 3 on anengaging sleeve 4. An engaging ring 5 with outer engaging, teeth 6 issolidly joined to a gear (not shown) rotatably mounted on the shaft. Asynchronizing cone 7 with an outer conical frictional surface 8 isjoined to the engaging ring 5. A synchronizing ring 9 is arrangedconcentrically with the synchronizing cone 7 and is provided with africtional surface 10, which faces the frictional surface 8 of thesynchronizing cone 7. In the embodiment shown, the synchronizing ring 9is provided with blocking elements 11 with cam surfaces 12, which in aknown manner cooperate with a cam surface 13 on ramps 14 on the engagingsleeve 4. In addition to the components described, the synchronizer alsocomprises known spring-loaded locking bodies (not shown).

According to the invention, the torque of the synchronizing ring 9 istransmitted to the engaging sleeve 4 via a torque-transmitting element,generally designated 20, which comprises a sleeve 21 with a number, e.g.three, of arms or fingers 22 received in slots 23 in the guide sleeve 1and having at their ends heels 24 with V-shaped cam surfaces 25, whichcooperate with corresponding cam surfaces 26 on the ramps 14. In theexample shown, the cam surfaces 25, 26 form an angle of 60° with theaxial direction of the gearbox, but the angle can vary within theinterval circa 40°-75°. The cam surfaces 12,13 in the example shown havea somewhat smaller angle relative to the axial direction, but it canalso have the same angle as the cam surfaces 25, 26.

Each finger 22 is provided with an axial projection 27 which engages anindividual cavity 28 in the synchronizing ring 9. Thetorque-transmitting ring has a radial flange 29 and a spring washerpackage consisting of two spring washers 30 lying between the flange 29and an opposing surface 31 on the guide sleeve 1.

The synchronizer according to the invention functions as follows:

FIGS. 2a and 2b show the various components in the neutral position.When engaging a gear, which means locking a gear (not shown), which isjoined to the engaging ring 5 shown at the right of the figure, theengaging sleeve 4 is moved to the right. The synchronization ring 9 ishereby displaced to the right under the influence of the blockingelements (not shown) and its friction surface 10 will come intofrictional engagement with the frictional surface 8. The result will bethat the synchronizing ring 9 turns and with it the torque-transmittingelement 20 (see FIG. 3) so that initially the cam surfaces 25 of theheels 24 will come into contact with the cam surfaces 26 of the ramps 14(FIG. 3). The torque-transmitting element 20 will gradually turnrelative to the engaging sleeve 4, and the cooperating cam surfaces 25,26 will cause the torque-transmitting element 20 to be pressedbackwards, compressing the spring washers 30, so that the componentswill assume the positions shown in FIGS. 4a, 4b. The springs 30 can inthis case be dimensioned so that in the compressed state they exert aforce of circa 1500 N in the engaging direction.

After completed synchronization in accordance with FIGS. 4a, 4b, therewill be a twisting loose and engagement as illustrated in FIGS. 6 and 7under the influence of the force of the spring package 30.

During the process described above, the synchronization itself takesplace in a conventional manner by the cam surfaces 13 of the ramps 14,lying closest to the synchronizing ring 9, coming into contact with thecorresponding cam surfaces 12 on the blocking elements 11 of thesynchronizing ring.

The invention has been described with reference to the components on theright-hand side of the guide sleeve 1. There will of course be thecorresponding function when shifting, involving locking of the engagingring 5 to the left of the guide sleeve 1. The ring 20 of the left-handtorque-transmitting element has fingers (not shown) which are angularlydisplaced relative to the fingers 22 on the right-hand element 20.

In an alternative embodiment, which is shown in FIGS. 8A and 8B, thesynchronizing device is made without the spring washer package. Atorque-transmitting element 31, which is simplified in comparison to theelement 20, comprises a sleeve 32 with a number, e.g. three, of innerfingers or pins 33, which are axially movable relative to, butrotationally fixed relative to, a synchronizing ring 34 and with anumber, e.g. three, of outer fingers or arms 35 which at their ends haveheels 36 with V-shaped oriented cam surfaces 37, which cooperate withcorresponding cam surfaces 38 on ramps 39 on the engaging sleeve 4. Thefunction is, except for the spring function, analogous to that of theembodiment described above.

What is claimed is:
 1. Synchronizer in a vehicle gearbox comprising aguide sleeve, intended to be non-rotatably joined to a shaft in thegearbox, an engaging sleeve which is non-rotatably, but axiallydisplaceably, mounted on the guide sleeve, an engaging ring providedwith exterior engaging teeth and which is intended to be securely joinedto a gear rotatably mounted on said shaft and is lockable relative tothe guide sleeve by axial displacement of the engaging sleeve from aneutral position to an engagement position, in which interior engagingteeth on the engaging sleeve engage the exterior teeth on the engagingring, and a synchronizing ring cooperating with the engaging sleeve andthe engaging ring, said synchronizing ring having a conical frictionalsurface which is movable to engagement with a facing conical frictionalsurface on a ring rigidly attached to the engaging ring, means beingarranged to amplify the engaging force upon displacement of the engagingsleeve from the neutral position to an engagement position, wherein thesynchronizing ring (9;34) is fixed rotationally relative to atorque-transmitting element (20;31), which is axially movable relativeto the synchronizing ring and has cam surfaces (25;37) which cooperatewith cam surfaces (26;38) on the engaging sleeve (4) and which uponrelative rotation between the torque-transmitting element and theengaging sleeve, caused by frictional engagement between the frictionalsurfaces of the synchronizing ring and the engaging ring, create a forceacting on the engaging sleeve in the engaging direction.
 2. Deviceaccording to claim 1, wherein the torque-transmitting element (20) ismovable in the direction away from the synchronizing ring against theeffect of a spring force.
 3. Device according to claim 2, wherein thetorque-transmitting element (20) has engaging teeth (27) engaginggrooves (28) in the synchronizing ring (13) and radial fingers (22)received in slots (23) in the guide sleeve (1) and that said camsurfaces (25) are formed at distal ends of the fingers.
 4. Deviceaccording to claim 3, wherein each finger (22) at its distal end has aheel (24), which is made with a pair of V-oriented cam surfaces (25)facing the synchronizing ring, and that the engaging sleeve (4) for eachheel has a pair of cam elements (14), which, in the neutral position,lie on either side of the associated heel and each have a cam surface(26) complementary to the facing cam surfaces (25) on the heel. 5.Device according to claim 3, wherein compression springs in the form ofspring washers (30) are arranged between an abutment surface on a sleeveof the torque-transmitting element (20) and a facing surface on theguide sleeve (1).
 6. Device according to claim 1, wherein thetorque-transmitting element (31) comprises a sleeve (32) with a numberof inner fingers (33), which are axially movable relative to, but arerotationally fixed relative to, the synchronizing ring (34), and with anumber of outer fingers (35), which at their ends have V-oriented camsurfaces (37) cooperating with the cam surfaces (38) of the engagingsleeve.